Perimeter: trace the boundary you intend to measure

A shape with interior lines can tempt children to add every visible segment. Trace the outer boundary first, then connect each measured side to that path so the total answers the intended question.

Trace the outside boundary once before adding side lengths. Internal lines do not contribute to the outer perimeter of the selected shape.

One complete trip around the outside

1. Follow the full outside boundary.
2. List its edge lengths.
3. Add each boundary segment once.

A rectangle measuring 4 units by 3 units has perimeter 4 + 3 + 4 + 3 = 14 units.

Perimeter and covered surface area answer different questions.

Did every outside segment appear once? Trace the edge with a movable marker.

Resources

• Reflection Journal Template — Use the blank reflection space for observations; write the measurement units and setup separately.

Further reading

• ASIC Moneysmart — teaching lesson plans
• Australian Curriculum Version 9 — Mathematics

Read next

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• Read a temperature record with its unit and context
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